While researching stuff connected with Eshell and shells in Emacs in general, I encountered an interesting bit of information. It doesn’t seem to be useful for me personally, since I seldom use M-x shell or M-x term, prefering Eshell instead, but maybe someone may find a use for it. When you run a script/command from one of those Emacs non-elisp shells, the environment variable INSIDE_EMACS is set to a nonempty value so that scripts can recognize that they run inside Emacs.